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Biometric Authentication App 🛡️

A modern React Native mobile application built with Expo and SDK 50+ demonstrating how to implement secure biometric authentication (Face ID, Fingerprint, and Iris Scan) for both iOS and Android.

📱 Overview

This app provides a boilerplate for implementing a "Security First" flow. It checks for hardware compatibility, verifies if biometrics are enrolled, and triggers the native OS authentication prompts.

Key Features

• Device Support Check: Detects if the device has biometric hardware.
• Enrollment Check: Verifies if the user has fingerprints or faces registered.
• Cross-Platform: Seamless Face ID for iOS and Fingerprint/Face unlock for Android.
• Graceful Fallback: Support for device PIN/Passcode if biometrics fail.
• Modern UI: Built with Lucide-react-native icons and clean layout.

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🚀 Getting Started

Prerequisites

• Node.js (v18 or newer)
• Expo Go app on your device (for basic testing)
• EAS CLI installed globally (npm install -g eas-cli)

Installation

1. Clone the repository

   git clone https://github.com/SasadaSaumya/biometric-auth-app.git
   cd biometric-auth-app

2. Install dependencies

   npm install

3. Configure permissions Ensure your app.json includes the Face ID permission (already configured in this repo):

   "ios": {
     "infoPlist": {
       "NSFaceIDUsageDescription": "Allow BiometricAuth to use Face ID for secure login."
     }
   }

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🛠️ Project Structure

├── assets/               # Static files (images/icons)
├── src/
│   ├── services/         
│   │   └── authService.js # Biometric logic & Hardware checks
│   └── screens/          
│       ├── LoginScreen.js # Entry screen with auth trigger
│       └── HomeScreen.js  # Protected content (Post-auth)
├── App.js                # State management & Navigation
├── app.json              # Expo configuration
└── package.json

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🧪 Testing Guide

Android

You can test on a physical device or an emulator.

• For emulators: Go to Extended Controls (...) > Fingerprint to simulate a touch.

npx expo start

iOS (Face ID)

Important: Face ID cannot be tested in the standard "Expo Go" app from the App Store because it requires a custom Info.plist. To test Face ID, you must create a Development Build:

1. Create a build (requires a free Expo account):

   npx expo run:ios
   # OR for a cloud build:
   eas build --profile development --platform ios

2. Install the resulting build on your device/simulator.
3. Start the dev server:

   npx expo start --dev-client

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📦 Key Libraries Used

• expo-local-authentication: The core biometric library.
• lucide-react-native: Beautiful, lightweight icons.
• expo-secure-store: (Recommended for production) To store sensitive tokens after authentication.

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🛡️ Security Best Practices (2026)

1. Level Verification: This app checks for BIOMETRIC_STRONG. Always ensure you aren't allowing "Weak" biometrics (like 2D face photos) for sensitive actions.
2. Fallback: Always provide a manual Password/PIN option in case the biometric hardware is damaged.
3. No Local Storage: Never store "True/False" login status in AsyncStorage. Use a secure token that is only released upon successful biometric callback.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

👤 Author

Sasada Saumya

• GitHub: @SasadaSaumya
• LinkedIn: SasandaSaumya